This invention relates to forage harvesters and more particularly relates to a shear bar for use with a rotary cutterhead.
Forage harvesters for removing crop material from the field, reducing the crop material in size and discharging the reduced crop into a collector vehicle are well known. Most currently marketed forage harvesters utilize a cylinder or reel type cutterhead and a stationary shear bar for cutting. Crop material is fed across the upper surface of the shear bar toward the rotating cutterhead which chops the crop into small particles. A cutterhead of this type is disclosed in the U.S. Pat. No. 4,061,284.
The shear bar is generally fastened to a strong support structure to insure that the shear bar can withstand the forces encountered during the cutting operation. To eliminate vibration and failure of the shear bar and/or its support, it is important to maintain contact between the shear bar and its support along the entire length of the shear bar. One known method (see. e.g., U.S. Pat. No. 3,342,231) for maintaining such contact is to use a support structure with a curved or crowned upper surface and rectangular shear bar with planar sidewalls. The shear bar is mounted by bending it over the curved support surface into an arched shape thereby providing good contact over the entire length of the shear bar. The arched upper surface is perpendicular to the shear bar surface across which crop material is fed for cutting. However, it has been found when using an arched shear bar that the clearance between the shear bar and cylinder circumscribed by the cutterhead varies sufficiently to reduce the uniformity of cut and frequently the harvester cutting efficiency. Both harvester efficiency and uniformity of cut are important design criteria for forage harvesters.